1. Field of the Invention
The present invention relates to an image display apparatus and, more particularly, to the image display apparatus suitably applicable to display apparatus called head-mounted displays (HMDs) and goggle type displays.
2. Related Background Art
A variety of proposals have been made heretofore about the image display apparatus of the head mounted type, so called the head-mounted displays (HMDs), constructed to guide image information displayed on such an image display element as a liquid crystal panel or the like, through a display optical system so as to permit an observer to observe an enlarged, virtual image thereof.
Japanese Patent Application Laid-Open Nos. 7-181391 and 9-258104 suggest the HMDs using a prism and a diffraction optical element as a scanning optical system.
These are constructed in such structure that the image information displayed on a liquid crystal display (LCD) is observed through an eyepiece optical system composed of a combination of a prism optical system with another lens system.
Japanese Patent Application Laid-Open No. 9-258104 describes the HMD wherein the eyepiece optical system includes a decentered prism having decentered surfaces with curvature and wherein an optical element including a diffractive surface with reciprocal dispersion characteristics of the large Abbe""s number of xe2x88x923.45 (hereinafter referred to as DOE) is placed between the LCD and the decentered prism or between the decentered prism and the eye (observer), thereby canceling chromatic aberration occurring in the decentered prism.
Japanese Patent Application Laid-Open No. 7-181391 describes the HMD wherein the eyepiece optical system is a combination of a normal prism with a refracting lens (and thus is not a decentered optical system) and wherein the DOE is adopted for a surface of the prism or the refracting lens in order to correct for chromatic aberration well.
As seen from the numerical examples of these applications, they both employ the DOE having a rotationally symmetric phase distribution on a rotationally symmetric surface.
Since the apparatus is mounted on the observer""s head, it has been desired heretofore that the image display apparatus for the HMDs be compact and lightweight and permit good observation of the display image on the display means.
In the image display apparatus disclosed in Japanese Patent Application Laid-Open No. 9-258104, the decentered prism is small and the display optical system can be made very thin. However, if this display optical system is composed of both the optical element with the DOE surface and the decentered prism, it will tend to become large.
It will also require highly accurate adjustment between the two members in the assembling process. Since the apparatus described in Japanese Patent Application Laid-Open No. 7-181391 uses the normal prism instead of the decentered optical system, the thickness of the entire optical system tends to be large.
An object of the present invention is to provide a compact optical system permitting easy correction for the decentering chromatic aberration and observation of image information displayed on the display means with high image quality, and an image display apparatus using it.
A prism body according to one aspect of the present invention is a prism body having a positive refractive power and having three or more optical surfaces, inclusive of a decentered optical surface with curvature, wherein said optical surfaces comprise a diffracting surface having a rotationally asymmetric phase distribution.
In a further aspect of the present invention, said diffracting surface is provided in said decentered optical surface with curvature.
In a further aspect of the present invention, said prism body comprises a plurality of reflecting surfaces with curvature.
In a further aspect of the present invention, said diffracting surface has a symmetric phase distribution on a cross section normal to a cross section in which said optical surface is decentered.
In a further aspect of the present invention, at least one of said reflecting surfaces is a surface with refractive powers differing depending upon azimuthal angles.
In a further aspect of the present invention, said prism body comprises an optical surface with curvature having both transmitting action and totally reflecting action.
In a further aspect of the present invention, said prism body comprises a first transmitting surface to which light is incident, a first reflecting surface which totally reflects light from the first transmitting surface, a second reflecting surface which reflects reflected light from the first reflecting surface, and a second transmitting surface which has the same shape as the first reflecting surface and which transmits reflected light from the second reflecting surface.
In a further aspect of the present invention, the first transmitting surface or/and the second reflecting surface of said prism body are diffracting surfaces having a rotationally asymmetric phase distribution.
In a further aspect of the present invention, said diffracting surface having the rotationally asymmetric phase distribution is provided in a transmitting surface.
A prism body according to a further aspect of the present invention is a prism body having a positive refractive power and having three or more optical surfaces, inclusive of a decentered optical surface with curvature, wherein the optical surfaces comprise a diffracting surface having a rotationally symmetric phase distribution on a surface with refractive powers differing depending upon azimuthal angles.
A prism body according to one aspect of the present invention is a prism body having a positive refractive power and having three or more optical surfaces, inclusive of a decentered optical surface with curvature, wherein the optical surfaces comprise a diffracting surface having a rotationally asymmetric phase distribution on a surface with refractive powers differing depending upon azimuthal angles.
An image display apparatus according to one aspect of the present invention is an image display apparatus wherein, using the prism body described above, light from display means displaying image information is guided to the pupil position of an observer to permit the observer to observe the image information displayed on the display means.
In a further aspect of the image display apparatus of the present invention, the light from said display means is guided to the observer without forming an intermediate image in said prism body.
An image display apparatus according to one aspect of the present invention is an image display apparatus wherein, using the prism body described above, light from display means displaying image information is guided to the pupil position of an observer and one optical surface of the prism body is comprised of a half mirror surface, whereby the observer is permitted to observe both the image information displayed on the display means and image information of the outside through the half mirror surface, in a common field.
An optical system according to one aspect of the present invention is an optical system comprising a plurality of decentered, reflecting surfaces with curvature, said optical system comprising a diffracting surface having a rotationally asymmetric phase distribution.
In a further aspect of the optical system of the present invention, at least one of said reflecting surfaces is a surface with refractive powers differing depending upon azimuthal angles.
In a further aspect of the optical system of the present invention, said diffracting surface having the rotationally asymmetric phase distribution is provided in a transmitting surface.
In a further aspect of the optical system of the present invention, said optical system comprises a prism body and an optical member, wherein said prism body has three or more optical surfaces, inclusive of a decentered optical surface with curvature.
In a further aspect of the optical system of the present invention, said diffracting surface is provided in a surface forming said prism body.
In a further aspect of the optical system of the present invention, said diffracting surface is provided in a surface of said optical member.
An image display apparatus according to one aspect of the present invention is an image display apparatus wherein, using the optical system described above, light from display means displaying image information is guided to the pupil position of an observer to permit the observer to observe the image information displayed on the display means.
In a further aspect of the image display apparatus of the present invention, the light from said display means is guided to the observer without forming an intermediate image in said optical system.
An image display apparatus according to one aspect of the present invention is an image display apparatus wherein, using the optical system described above, light from display means displaying image information is guided to the pupil position of an observer and one optical surface of the optical system is a half mirror surface, whereby the observer is permitted to observe both the image information displayed on the display means and image information of the outside through the half mirror surface, in a common field.
An optical system according to one aspect of the present invention is an optical system comprising a plurality of decentered, reflecting surface with curvature, said optical system comprising a diffracting surface having a rotationally symmetric phase distribution on a surface with refractive powers differing depending upon azimuthal angles.
An optical system according to one aspect of the present invention is an optical system comprising a plurality of decentered, reflecting surface with curvature, said optical system comprising a diffracting surface having a rotationally asymmetric phase distribution on a surface with refractive powers differing depending upon azimuthal angles.
A prism body according to one aspect of the present invention is a prism body comprising an optical surface having rotationally asymmetric, transmissive-refractive powers or reflective-refractive powers, and a diffracting surface having a rotationally asymmetric phase distribution.
In the prism body according to a further aspect of the present invention, said optical surface and said diffracting surface are a common surface or different surfaces.
A prism body according to one aspect of the present invention is a prism body comprising an optical surface having rotationally asymmetric, transmissive-refractive powers or reflective-refractive powers, and a diffracting surface having a rotationally symmetric phase distribution.
In a further aspect of the present invention, said optical surface and said diffracting surface are a common surface or different surfaces.